1. Technical Field
Embodiments of the present disclosure relate to focus apparatus and, more particularly, to a focus apparatus of an image measuring system.
2. Description of Related Art
Auto-focus systems are used in optical measuring instruments, such as in image measuring systems. Generally, the auto-focus systems include an illuminator used to generate and emit light to a test object, so as place focus on the test object. However, the illuminator also generates considerable thermal energy when it emits light. The thermal energy may influence the wavelength of the light. For example, if the temperature of the illuminator is 25 degrees Celsius, the wavelength of the light may be 450 nanometers; if the temperature of the illuminator is 95 degrees Celsius, the wavelength of the light may be 700 nanometers. As a result, it is difficult to precisely focus on the test object if the wavelength of the light is changed intensely. More importantly, if the light which is projected on the surface of the test object is not uniform, it may also be difficult to precisely focus on the test object.
What is needed, therefore, is an improved focus apparatus of an image measuring system.